The nice thing with believing in no objective morality is that you needn't to solve such poorly intelligible questions. I hope Eliezer is trying to demonstrate the absurdity of believing in objective morality, if so, then good luck!

"I mean... if an external objective morality tells you to kill babies, why should you even listen?" - this is perhaps a dangerous question, but still I like it. Why should you do what you should do? Or put differently, what is the meaning of "should"?